Fluid-structure Interaction Numerical Model Research Articles

Numerical investigation on dynamic characteristics of oil-water annular flow-induced vibration in curved pipes

To improve the stability of water-lubricated transportation and reliability of pipes in service, the fluid–structure interaction numerical model has been established to investigate the dynamic characteristics of oil-water annular flow-induced vibration in curved pipes and the effect of main parameters in this study. The results illustrate that a single vibration mode of curved pipes is excited by oil-water annular flow, and there exists no multi-modality due to the limited pulsation of pressure and interface of two-phase flow. The change of velocities and oil-water ratios leads to change of flow pattern, making the dynamic response severer. When the oil-water ratio is larger than 2.035, its effect is greater than velocity. The physical properties of oil have a significant effect on the dynamic response. The root-mean-square dimensionless displacement AY,RMS/D and maximum dimensionless displacement AY,MAX/D of fuel oil-water annular flow-induced vibration decrease to 75.6% and 76.5% respectively, which means that the increase of dynamic viscosity reduces the fluid force and suppresses the vibration. AY,RMS/D and AY,MAX/D increases by 1.62 times when the bending angle θ increases from 30° to 90°, indicating that the increase of bending angles also leads to the severer dynamic response.

An investigation into the micro-geometric tapered-shape surface design of the piston bore of a piston–cylinder interface in an axial piston motor

Abstract. In pursuit of design solutions that reduce energy loss and improve wear resistance for the piston–cylinder interface in an axial piston motor, a fluid-structure interaction numerical model and a new test rig of the friction force of the piston–cylinder pair are developed to achieve the analysis and design of the micro-geometric tapered-shape surface of a piston bore. The piston bore with the tapered-shape surface axial distribution length ratio of 49.44 % of the overall length is found to be the relatively optimized one. Furthermore, how the shaft speed, load pressure, and swash plate angle influence the performance of the two-type interface is analyzed. Numerical analysis results show that, compared with the traditional cylindrical piston bore design, the piston–cylinder interface with the optimized tapered-shape piston bore in the axial piston motor can achieve a significant reduction in leakage flow and friction force, and the experimental results are consistent with the simulation results.

Computational aeroacoustics in flexible conduits with application to biomedical fluid dynamics

Flexible tubes are simple yet powerful tools for the modeling of respiratory and circulatory systems [1, 2]. In the last decade, access to high-performancecomputational resources has allowed the implementation of realistic numerical models of human vessels based on Computational Fluid Dynamics (CFD) and Fluid-Structure Interaction (FSI) simulations. Interestingly, the recently proven correlation [3] between CFD observables (like the pharyngeal airway's resistance) and clinical data (such as the Apnoea Hypopnea Index in Obstructive Sleep Apnoea patients) suggests a possible development of diagnostic methods based on numerical simulations. This work aims to investigate the extension of these correlations to the aeroacoustics characteristics of flexible conduits by means of a fully coupled FSI numerical model based on the Large Eddy Simulation method. These results have relevant applications to studying diseases of the human upper vocal tract, voice production, obstructive sleep apnoea, and adventitious lung sounds, such as wheezing and crackling. [1] Grotberg, J. B., & Jensen, O. E. (2004). Annu. Rev. Fluid Mech., 36, 121–147. [2] Schwartz, A. R., & Smith, P. L. (2013). The Journal of physiology, 591(Pt 9), 2229. [3] Schickhofer L., Malinen J., Mihaescu M., J. Acoust. Soc. Am. - JASA, 145 (4): 2049–2061, 2019. https://doi.org/10.1121/1.5095250

Verification of fluid-structure interaction modelling for wave propagation in fluid-filled elastic tubes

This paper presents a verification study of wave propagation in fluid-filled elastic tubes using a coupled numerical simulation method by comparing the simulation results with analytical solutions. A three-dimensional fluid-structure interaction numerical model is built using Ansys software. Wave propagation is investigated by applying a pressure pulse at the inlet of a fluid-filled elastic tube. The speed of the pressure wave and the radial displacement of the tube are simulated and compared with theoretical values. Simulation results yield a high level of accuracy. Different structural elements are used to represent the tube, and their impact on the results is discussed. The effects of tube material, tube constraints and fluid properties are also investigated in this study.

Investigation of whipping effect on high energy pipe based on fluid-structure interaction method

A fluid-structure interaction numerical model has been established to investigate the whipping effect on high energy pipe in this study. The validation test has been performed by the comparison with the experimental results and it is found that the fluid-structure interaction model can well predict the displacement and the maximum restraint force of the piping system. Then, the dimensionless displacement of the cantilever pipe and U-bolt restraints, the maximum restraint force and the maximum strain energy are used to evaluate the effect of flow rate, pulsation frequency, overhang length, initial clearance and friction coefficient on the whipping effect. The results illustrate that the dimensionless root-mean-square displacement of the cantilever pipe and U-bolt restraints increase to 5.31 times and 9.41 times, respectively as the flow rate increases. The mode transition phenomenon occurs as the flow rate increases to over 180 kg/s and 284 kg/s, respectively. When the pulsation frequencies are close to the first natural frequency of the cantilever pipe, the resonance effect can enhance the whipping effect and enlarge the displacement of U-bolt restraints. The increase of overhang length, initial clearance and friction coefficient can also intensify the whipping effect.

Numerical Study of Flat Plate Impact on Water Using a Compressible CIP–IBM–Based Model

Due to the entrapment of compressible air, the process of a flat plate impact on water is complicated, which cannot be reproduced using incompressible simulations. To investigate such a slamming process, an accuracy compressible fluid–structure interaction numerical model has been proposed. The solution of this model is based on the constrained interpolation profile (CIP) method to solve the Navier–Stokes equations for the computation of fluid, and an implicit immersed boundary method (IBM) is used to calculate the fluid–structure interaction. Firstly, the present (CIP–IBM–based) model is validated against the problem of the flow past a stationary cylinder. Then it is implemented to simulate the problem of a rigid flat plate impact on water. The predicated impact pressure is compared with reference experiments and other simulations. The CIP–IBM–based model shows a better performance in dealing with sub-atmospheric pressure and reloading. From the numerical view, it is shown that the oscillation of the slamming pressure is significantly affected by the compression and expansion of the entrapped air cushion, and under the influence of the air cushion, the slamming pressure distribution along the bottom is not constant, which also varies greatly with time.

A novel coupled Riemann SPH–RKPM model for the simulation of weakly compressible fluid–structure interaction problems

This paper established a novel Riemann SPH–RKPM fluid–structure interaction numerical model, which is more stable and has lower dissipation than the traditional method. Firstly, an improved dissipation limiter is proposed and applied to Riemann SPH to simulate fluid motion, effectively reducing dissipation while ensuring computational stability. Secondly, an improved method to treat the fluid–structure interaction (FSI) force is proposed, which introduces the Riemann solver into the normal flux method to solve the FSI force. This improvement ensures the smoothness of the flow field pressure at the fluid–structure interface and then improves the stability of the violent impact fluid–structure interaction problem. This paper used the RKPM to solve the large deformation of the structure. Several benchmark tests and one improved example are used to verify the convergence and accuracy of the numerical model. The results calculated in this paper agree with experiment and other numerical methods, proving that the Riemann SPH–RKPM fluid–structure interaction numerical model is effective and has high accuracy.

A comparison of Newtonian and non-Newtonian pulsatile blood rheology in carotid bifurcation through fluid–solid interaction hemodynamic assessment based on experimental data

Endothelial cells play a crucial role in the arterial homeostasis. In addition to physiological risk factors, abnormal levels of hemodynamic parameters induced by the pulsatile flow contribute to atherosclerotic plaque formation and development. In this study, we used an experimental setup to study the hemodynamics of Newtonian and non-Newtonian blood flow on a deformable model of human carotid bifurcation. The flow/pressure pulses of the experimental model were fed into a fluid–structure interaction numerical model, and respective hemodynamic parameters were obtained and compared between the two flow regimes. Results revealed noticeable differences among the two flow regimes when the pulsatile nature of blood flow and pressure were considered, with more distinct differences near junction sites. Velocity profiles of the non-Newtonian model were more flattened with higher back flow during the diastole. The shear stress waves as well as shear-dependent parameters, such as oscillatory shear index, relative residence time, and vorticity, as well as wall stress and strain, also indicated significant differences among the two models. Regardless of flow regime, results showed a good agreement with clinical outcomes in human carotid bifurcation, especially the carotid sinus. Near the bifurcation, marked fluctuations of shear stress are evident. Around the junction site, wall pulsation experienced variations up to five times of the normal pulse span. The quantified hemodynamic parameters obtained from proposed accurate model of carotid bifurcation may help to achieve technological solutions to adjust the out of biological ranges of these parameters, and avoid atheroma formation or treat the diseased artery.

Experimental and Numerical Studies on the Development of Hysteresis in a Shock Absorber with a Shim Disc Valve

The paper describes the observed occurrence of hysteresis of the characteristic curve of a shock absorber valve. The phenomenon has an impact on the asymmetry of the damping force characteristic and should be taken into account when modelling the valve operation. The aim of the investigations was to determine the factors generating the phenomenon and establish the relationships between these factors and the hysteresis size. Tests were carried out on a stand intended for valve measurements in isolated conditions. A strongly coupled Fluid-Structure Interaction numerical model was also created to simulate the valve operation in selected conditions. The results indicate that the hysteresis loop occurrence is mainly due to the conditions of the valve disc stack preload in the process of its composition and, consequently, to the friction between the valve elements. Having an impact on the contact between discs and on the disc stack overall structure, they affect the hysteresis field significantly. The testing results confirm the supposition that hysteresis is not due to the phenomena related to the conditions of the flow through the valve.

Development, verification, and validation of comprehensive acoustic fluid‐structure interaction capabilities in an open‐source computational platform

AbstractThe acoustic fluid‐structure interaction (FSI) formulation is a practical numerical approach for the seismic analysis of fluid‐filled tanks. However, there are no verification and validation studies reported in the literature that demonstrate the ability of an acoustic FSI numerical model to predict responses important to structural and mechanical design for intense translational and rotational earthquake inputs. Herein, an acoustic FSI formulation is implemented in the open‐source Multiphysics Object‐Oriented Simulation Environment (MOOSE), and is formally verified and validated using analytical solutions and code‐to‐code verification, and experimental data, respectively. The analytical solutions are for small amplitude, unidirectional seismic inputs. The code‐to‐code verification utilizes a previously verified and validated Arbitrary Lagrangian‐Eulerian (ALE) numerical model in the commercial finite element code LS‐DYNA. The validation studies utilize a comprehensive data set assembled from results of 3D earthquake‐simulator tests of a fluid‐filled vessel. The acoustic numerical model in MOOSE is verified and validated for hydrodynamic pressures and support reactions except for cases that involve significant convective response. For small amplitude inputs, numerically predicted wave heights match those of the analytical solutions. The numerical model is not verified and validated for wave height calculations under intense 3D seismic inputs. The run times for the acoustic FSI simulations in MOOSE are an order of magnitude, or more, shorter than for the corresponding ALE simulations in LS‐DYNA. The utility of the MOOSE acoustic FSI implementation is demonstrated by seismic analysis of a building equipped with a fluid‐filled, advanced nuclear reactor.

Holding Force and Vertical Vibration of Emergency Gate in the Closing Process: Physical and Numerical Modelling

A two-dimensional unsteady fluid–structure interaction numerical model was established, based on the physical model test, to investigate the influence of vertical vibration on the holding force of an emergency gate in the closing process. Gate motion was controlled by the user-defined function in Fluent. Attention was paid to the relationship between the vertical vibration, hydrodynamic loads and flow discharge. The experiment results show that holding force has three typical forms in the closing process and it is related to the service gate height. The numerical model can reflect the gate vertical vibration and the gate-closing displacement in the form of steps. Gate vertical vibration in the closing process is a motion-induced vibration caused by gate active falling. Moreover, the transition from full-flow to open-flow behind the emergency gate has a great influence on the gate vertical vibration. With a small gate opening, gate vertical vibration makes the flow discharge fluctuation increase. Furthermore, flow discharge has an influence on the gate body loads, which is mainly concentrated in the upstream plate and gate bottom. Finally, the lift force coefficient at the gate bottom is different from the standard and is mainly controlled by the outflow boundary condition. The simulation result is in good agreement with the experiment and the relative error meets engineering requirements, suggesting that the numerical model can successfully simulate the gate fluid–structure interaction and reproduce the characteristics of physical quantities in the closing process.

Experimental and numerical investigation of the fluid-structure interaction on a flexible composite hydrofoil under viscous flows

This research investigates the fluid-structure interaction and hydroelastic response of a composite hydrofoil using an innovative joint experimental and numerical method. The main novelties are, first, the use of a state-of-the-art strain measurement technique, via a fully-distributed-optical fiber sensor directly embedded within the composite plies. This method allows for a finer representation of the structural deformations under hydrodynamic loading. Second, a tightly-coupled high-fidelity fluid-structure interaction numerical model taking into account the turbulent effects in the flow and the ply-by-ply modelling of the composite, is compared to the experimental results. A composite profile is specifically designed as a trapezoidal hydrofoil and is tested for moderate Reynolds number and pre-stall and post-stall incidences. High-speed imaging of the hydrofoil tip and vibrometer measurements are carried out to determine the experimental tip displacements and hydrofoil's vibrations. The numerical and experimental results show a very strong hydroelastic response, with a structural resonance even for low Reynolds numbers due to the high flexibility of the structure. Strong coupling of the fluid and the structure, with lock-in of the von Kármán vortex-shedding to the structure for small incidences, and an excitation of the structure by leading-edge vortex-shedding for higher incidences, are also observed.

Numerical modeling and analysis of heat transfer for floatation nozzle with a flexible substrate

Floatation nozzle is employed to guide the flexible substrate without contact in simultaneous double-sided coating. The deformation of the flexible substrate is significant to the flow and thermal fields. The heat transfer for floatation nozzle with a flexible substrate is studied in this paper. A fully-coupled fluid-structure interaction numerical model is developed to investigate the heat transfer characteristics and deformation for floatation nozzle with a flexible substrate. The fluid domain is updated by diffusion-based smoothing dynamic mesh formulation that is fully coupled to the deformation of the flexible substrate. The deformation profile of flexible substrate coupled to fluid domain is approximated by cosine series, and the coefficients in cosine series are calculated by Galerkin least square method. The steady state solutions of floatation nozzle with a flexible substrate can be obtained by a pseudo transient approach. The numerical results show that the deformation of flexible substrate changes the relative magnitude of potential core length and nozzle-to-plate distance. The size increase, position move and disappear of recirculation bubbles of flexible substrate change the streamline, turbulence intensity, temperature distributions. Three peaks of heat transfer coefficient for rigid substrate are observed and the mechanisms are elucidated. The average heat transfer coefficient of flexible substrate is larger than that of rigid substrate, although the maximum heat transfer coefficient of flexible substrate is smaller. Furthermore, a significant decrease of centerline pressure of flexible substrate is observed. Reynolds number and inlet width are the most significant parameters influencing the flow and thermal fields.

Effect of local geometrical imperfection on dynamic buckling of cylindrical storage tanks

Steel cylindrical tanks are the most susceptible to damage due to dynamic buckling during earthquakes. The production of cylindrical shell without imperfections is very difficult or sometime even impossible. The most previous research to study the geometrical imperfection in the shell of steel tanks using various methods did not deal with the fluid–structure interaction (FSI) and the dynamic loads. In this paper, the FSI numerical model is used to estimate the effect of local geometrical imperfection with dynamic buckling of fluid-filled tanks. The liquid inside the tank was modeled using specific Ansys’s finite elements and fluid–structure interaction. The calculation includes modal and time history analysis, including material and geometric nonlinearity. Then a typical cylindrical tank is analyzed by the application of three different stability criteria to estimate the critical PGA. The obtained dynamic buckling results of the perfect and imperfect tank are compared. The effect of geometrical imperfection on dynamic buckling is clearly shown. The PGAcr of the imperfect tank models decreases by 09.11%.

Dynamic mechanism of phase differences in One degree-of-freedom vortex-induced vibration of a cylindrical structure

The purpose of this study is to provide some insights into the phase mechanism of a cylindrical vortex–induced vibration. A transient coupled fluid–structure interaction numerical model is adopted to simulate a cylindrical vortex–induced vibration. The vortex shedding around the cylinder is investigated numerically by a two-dimensional large eddy simulation approach which can catch more details of the flow field and more accuracy on computing hydrodynamic forces. The vortex shedding modes and response and hydrodynamic forces of a cylindrical vortex–induced vibration are acquired with varied frequency ratios. According to differences in the vortex shedding location, the vortex wake can be characterized by two kinds of mode, the “first mode” and the “second mode.” The mechanisms behind the phases of the first mode and the second mode vortex wakes are investigated, and it is found that the flow speed induced by a cylindrical transverse vibration and the position of a vortex release are the root causes of the phase difference between the lift coefficient and transverse displacement. The speeds caused by a cylinder vibration and a cylinder-shed vortex are the reasons that the lift amplitude of an oscillatory cylinder is different from that of a fixed cylinder.

Two degree of freedom flow-induced vibration of cylindrical structures in marine environments: frequency ratio effects

The flow-induced vibration of a cylindrical structure is a very common problem in marine environments such as undersea pipelines, offshore risers, and cables. In this study, the vortex-induced vibration (VIV) of an elastically mounted cylinder at a low Reynolds number is simulated by a transient coupled fluid–structure interaction numerical model. Considering VIV with low damping ratio, the response, hydrodynamic forces, and vortex shedding modes of the cylinder is systematically analyzed and summed up the universal rule under different frequency ratios. On the basis of the analysis, we find that the frequency ratio α is a very important parameter. It decides the locked-in, beat, and phase-switch phenomena of the cylinder, meanwhile, it also influence the vortex mode of the cylinder. The trajectory of the two degrees of freedom (2 DOF) case at different natural frequency ratios is discussed, with most trajectories having a “figure of 8” shape and a few having a “crescent” shape. A fast Fourier transformation technique is used to obtain the frequency characteristics of the vibration of the cylindrical structure. Using the 2 DOF cylinder model in place of the 1 DOF model presents several advantages in simulating the nonlinear characteristics of cylindrical structures, including the capacity to model the crosswise vibration generated by in-line vibration.

Effects of natural frequency ratio on vortex-induced vibration of a cylindrical structure

In this study, vortex-induced vibration (VIV) of a circular cylinder at the low Reynolds number of 200 is simulated by a transient coupled fluid–structure interaction numerical model. The transient coupling between the fluid and the structure is updated by on-line transmission between fluid dynamic loads and structure response data. The structural vibration of the cylinder influences the flow around it, and the change of fluid flow in turn influences the response of the cylinder. The boundary layer near the cylinder is updated by dynamic mesh technology with grid updating at each time step. This method successfully simulates the vortex generation and the real-time flow field of the cylinder. Considering VIV with low reduced damping parameters, the trend of the lift coefficient, the drag coefficient and the displacement of cylinder are analyzed under different oscillating frequencies of the cylinder. The frequency ratio α is a very important parameter, when α is small (α=0.5), the amplitude of lift coefficient of an elastic cylinder is large and the response of cylinder is weak. With an increase in α, the lateral displacement of the cylinder increases, but the amplitude of lift coefficient decreases. The amplitude of the lift coefficient reaches its minimum value when α is between 0.9 and 1.2. After that, the amplitude of the lift coefficient begins to increase. The typical nonlinear phenomena of locked-in, beat and phase-switch can be captured successfully. The evolution of vortex shedding from the cylinder with varied α is discussed. The trajectory of the two degrees of freedom (2 DOF) case at different α is also discussed; all appear to have a “Fig. 8” shape. A fast Fourier transformation technique is used to obtain the frequency characteristics of the cylindrical structure vibration. Using the 2 DOF cylinder model in place of the one degree of freedom (1 DOF) cylinder model presents several advantages in simulating the nonlinear characteristics of cylindrical structures including the capacity to model the crosswise vibration generated by in-line vibration.

Capability of structural–acoustical FSI numerical model to predict natural frequencies of submerged structures with nearby rigid surfaces

Structural–acoustical model is used in industry to determine natural frequencies of runners and impellers in hydraulic turbomachinery in the stage of design. In these calculations the fluid domain is considered with comparable large distances to stationary parts while there are parts of the submerged structure (runner or impeller) that are extremely close (in relation to its thickness) to a rigid surface (hydraulic seals). These seals are not considered in the numerical model because it is assumed that structural–acoustical model is not capable to predict natural frequencies with nearby rigid surfaces. The present work builds a fluid structure interaction numerical model based on structural–acoustic coupling, checks the numerical model’s accuracy, and determines its capability to predict natural frequencies reduction due to nearby rigid surfaces comparing this model against experimental data of submerged cantilever plates. It is found that the structural–acoustical model can accurately predict the natural frequencies for submerged structures with nearby rigid surfaces with averaged absolute errors of 2.5%. This is an interesting result because it suggests that simulation of runners and impellers can be carried out considering the effect of hydraulic seals, therefore, obtaining natural frequencies that are closer to those found under operation.

The low Reynolds number limit of vortex-induced vibrations

Vortex-induced vibrations (VIV) of a circular cylinder at low values of the Reynolds number (Re) are simulated by means of a fully coupled fluid–structure interaction numerical model based on the finite element method. It is shown that VIV could occur far below the first Hopf bifurcation (Re<47). The main objective of this study is to determine the limiting curve that separates the non-vibrational area from the possible vibrations occurrence area in the Reynolds number–reduced velocity (Re, Ur) plane. We assume that by taking a zero mass cylinder and zero structural damping we should get the low limit of vibrations in terms of Re and Ur. It is shown that transverse vibrations could occur for reduced velocities larger than 40 and that for zero mass/no damping cylinders the maximum vibration amplitude for subcritical Reynolds numbers is obtained at Ur=6.5.

Validation of a numerical 3-D fluid–structure interaction model for a prosthetic valve based on experimental PIV measurements

A numerical 3-D fluid–structure interaction (FSI) model of a prosthetic aortic valve was developed, based on a commercial computational fluid dynamics (CFD) software program using an Arbitrary Eulerian Lagrangian (ALE) formulation. To make sure of the validity of this numerical model, an equivalent experimental model accounting for both the geometrical features and the hydrodynamic conditions was also developed. The leaflet and the flow behaviours around the bileaflet valve were investigated numerically and experimentally by performing particle image velocimetry (PIV) measurements. Through quantitative and qualitative comparisons, it was shown that the leaflet behaviour and the velocity fields were similar in both models. The present study allows the validation of a fully coupled 3-D FSI numerical model. The promising numerical tool could be therefore used to investigate clinical issues involving the aortic valve.